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Keywords:

  • Sjögren's syndrome;
  • Physical capacity;
  • Fatigue

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

Objective

To examine physical capacity (aerobic capacity, joint mobility, muscle function, and standing balance) in women with primary Sjögren's syndrome (primary SS) and to examine the correlation of aerobic capacity with fatigue, functional disability, and mental aspects (anxiety and depression).

Methods

Fifty-one women who fulfilled the European Community criteria for primary SS and who had anti-SSA/SSB antibodies or a positive lip biopsy were compared with 51 age-matched controls. Physical capacity, fatigue, functional disability, anxiety, and depression were investigated by means of questionnaires and clinical examinations.

Results

The women with primary SS had significantly decreased aerobic capacity (VO2max = 28.7 versus 32.4 ml/kg/minute; P = 0.013), shoulder mobility (58 versus 59 scale points; P = 0.003), grip strength (214 versus 259 N; P = 0.000), isokinetic strength of the knee flexors (51 versus 56 Nm; P = 0.049), endurance of the knee flexors (620 versus 712 J; P = 0.008), and standing balance (25 versus 28 seconds; P = 0.006) when compared with the reference group. For the primary SS patients, greater effort was needed to carry out the test of aerobic capacity, and they experienced more pain during the shoulder mobility test. Aerobic capacity correlated with the fatigue experienced (r = –0.33, P = 0.022) but not with functional disability or mental aspects.

Conclusion

The results indicate that women with primary SS have decreased physical capacity, which may be related to the experience of fatigue.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

Primary Sjögren's syndrome (primary SS) is a chronic, inflammatory, autoimmune disease of unknown etiology (1). Prevalence figures reported in the literature vary due to the fact that different classification criteria are used. According to the Copenhagen criteria (2), which require 2 abnormal objective test results for dry eyes and dry mouth, respectively, the prevalence of SS was 2.7% in a population study in Sweden for the age group 52–72 years (3). In a community-based study of adults aged 18–75 years in the United Kingdom, the prevalence of primary SS (autoimmune and nonautoimmune) was estimated to be 3.3% (4) using the European Community (EC) criteria (5). The EC criteria include 6 items (2 symptoms and 4 objective tests), and the diagnosis is based on the presence of at least 4 of them. The peak incidence is between 40 and 60 years and the occurrence in women is about 9 times that of men (1).

Primary SS is characterized by hypofunction of the exocrine glands, especially the lacrimal and salivary glands, which result in the key symptoms, namely, dry eyes and dry mouth (1). Nonexocrine symptoms, such as disabling fatigue, arthralgia, myalgia, and mental symptoms, are other common complaints of primary SS (4, 6–8).

Impaired physical capacity, including decreased aerobic capacity, joint mobility, and muscle function, is a common consequence of many rheumatic disorders, such as rheumatoid arthritis (RA) (9, 10), systemic lupus erythematosus (SLE) (11–13), and fibromyalgia (FMS) (14, 15). The documentation on physical capacity in primary SS is sparse. In 2 recent studies concerning functional disability and health-related quality of life in primary SS (16, 17), patients reported that they experienced impaired physical function, i.e., activities such as vacuuming, going up stairs, walking, bathing, and dressing. To the best of our knowledge, no studies have reported measurements of physical capacity based on clinical examinations in primary SS.

The primary aim of this controlled, cross-sectional study was to describe aerobic capacity, muscle function, standing balance, and joint mobility in women with primary SS, and to compare the results with those of a control group matched for age and sex. A second aim was to investigate whether aerobic capacity correlates with experienced fatigue, functional disability, and mental aspects.

SUBJECTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

Pilot study.

An initial pilot study was performed to investigate the statistical power of the measurement method for aerobic capacity. Ten women with primary SS with a mean age of 52.1 years (SD 11.3) and 10 healthy women with a mean age of 48.9 years (SD 11.4) were included.

Patients.

Sixty-three of all diagnosed patients with primary SS registered at the Sjögren research unit, Department of Rheumatology, Malmö University Hospital, Malmö, Sweden, fulfilled the following inclusion criteria: primary SS according to the EC criteria (5); increased levels for anti-SSA/SSB antibodies and/or autoimmune sialadenitis; woman born in 1935 or later; living in a defined area (4 counties in southern Sweden); a good knowledge of the Swedish language; no intercurrent, severe mental or somatic disease (e.g., severe heart disease); and not taking β-blockers. The patients were invited to the study by mail. After 1 week, they were contacted by telephone for an appointment. Fifty-one of the 63 women agreed to participate in the study and were included. The mean age was 49.0 years (SD 12.7) and the mean duration of dry eyes and dry mouth was 13.0 years (SD 9.8). Eighteen patients were on medication for other disorders (asthma, allergy, goiter, hypertension, gastric/intestinal problems, anxiety/depression) and 13 patients used pain relievers. Further characteristics of the patients are to be found in Table 1.

Table 1. Characteristics of the women with primary Sjögren's syndrome (SS) and the control group*
 SS group (n = 51)Control group (n = 51)P
  • *

    VAS = visual analog scale; IQR = interquartile range; ab = antibody. P values determined by paired t-test, Wilcoxon's signed rank sum test, or chi-square test.

  • Working = working part or full time; not working = retired, on sick leave, unemployed, or student.

  • Based on Saltin and Grimby (18).

Age, years, mean (SD)49.0 (12.7)49.0 (12.7)1.0
Weight, kg, mean (SD)65.9 (9.9)65.8 (9.7)0.95
Height, cm, mean (SD)165.1 (4.6)165.2 (5.8)0.88
Education, years, mean (SD)11.8 (3.1)12.3 (3.3)0.33
Duration of symptoms, years, mean (SD)13.0 (9.8)
Musculoskeletal pain, VAS 0–100, median (IQR)30 (11–59)0 (0–21)0.000
Married (cohabiting), no.30250.32
Working/not working, no.27/2436/150.067
Physically active, yes/no, no.40/1144/70.299
Level of physical activity, light/moderate/hard/elite, no.13/30/8/07/28/15/10.048
Smoker, yes/no/exsmoker, no.4/47/1014/37/110.023
Musculoskeletal pain, yes/no, no.40/1119/320.000
Hand arthralgia, yes/no, no.31/206/450.000
Medication for other disease/disorder, yes/no, no.18/3312/390.192
Pain relievers, yes/no, no.13/386/450.075
Autoimmune sialadenitis, no.41
Positive for anti-SSA/SSB ab, no.27
Autoimmune sialadenitis and positive for anti-SSA/SSB ab, no.17

Control group.

Control subjects were recruited from the National Population Records in Malmö, Sweden, and were matched for age and sex. Twelve subjects were taking medication for various disorders (asthma, allergy, goiter, diabetes, hypertension, anxiety/depression) and 6 subjects used pain relievers. For further characteristics, see Table 1

Assessment methods.

Questionnaire.

Before the test of physical capacity, patients and controls answered a questionnaire regarding age, marital status, work status, education, physical activity, smoking habits, medication, intercurrent diseases, and for the primary SS patients, duration of symptoms.

Aerobic capacity.

Åstrand's method (19) was used to calculate the maximum oxygen uptake (VO2max) during a submaximal workload provided by a bicycle ergometer (Monark 90818 E). The subjects performed the test with a pedal rate of 50 revolutions/minute. Work loads between 50 watts and 150 watts were used. The workloads were selected to elicit heart rates at steady state of at least 125 beats/minute (19). The exercise period was generally 6 minutes. Heart rate was measured at the end of every minute. The average value from the 5th and 6th minute was recorded if the difference between the 5th and 6th minute was ≤3 beats. Otherwise, the subject exercised until steady state was reached. The submaximal test predicts the maximal oxygen uptake of a subject based on measurements at submaximal level. It is assumed that there is a linear relation between the workload and the heart rate at steady state and that a certain amount of oxygen is required for each workload. The heart rate and corresponding work rate are used to estimate maximal oxygen uptake using the Åstrand-Rhyming nomogram with correction for age (19, 20). Reliability of Åstrand's method has been reported (intraclass correlation coefficient 0.93–0.96) (21). Exertion was rated on the Borg Rating of Perceived Exertion (RPE) scale, which is a tool for estimating effort and exertion during physical work (22). The RPE score of the last minute of the bicycle test was registered. The range of the RPE scale is 6–20, where 6 means no exertion at all and 20 means maximal exertion. The reliability of the RPE scale has been reported to be high (22).

Isokinetic muscle strength and endurance.

Isokinetic strength (concentric contraction with fixed angular velocity and changing load) and endurance were tested for the flexors and extensors of the right and left knee at velocities of 60°/second and 240°/second. The Biodex Multi-Joint Rehabilitation Equipment System 3 isokinetic dynamometer (Biodex Medical Systems, Shirley, NY) was used. Five maximal repetitions at 60°/second and 25 maximal repetitions at 240°/second were performed. The subject sat secured to the apparatus with 90° hip flexion, supported thigh, and arms crossed on the chest. The resistance pad was placed as distally as possible on the tibia. The knee joint range of motion was set to 15–95°. The right leg was measured before the left and extensors and flexors were tested in the same session. The subject rested for 20 seconds between the test sets. The peak torque (Nm) of 5 repetitions at 60°/second was used as a measure for muscular strength, and total work (J) at 240°/second was used as a measure for muscular endurance. The results are presented as the average of the sum of the values for right and left leg. Peak torque is the most properly studied isokinetic strength testing parameter (23), and for muscular endurance, total work in a 25-repetition test with a speed of 240°/second is recommended (23). The reproducibility for absolute endurance parameters has been shown to be high (24).

Standing balance.

Standing balance was assessed with the 1-legged, timed balance test (25). The subject stood on 1 leg at a time, without shoes, in a defined square on the floor, with arms folded across the chest and eyes open. The right leg was tested before the left and the goal was to balance for 30 seconds on each leg, this time span being an endpoint used by previous investigators (25). Timing started when the subject lifted 1 foot from the floor and stopped when a variation in the preestablished position occurred. The result is presented as the average of the value for both legs.

Grip strength.

The Grippit instrument (DeteKtor, Gothenburg, Sweden) (26) was used for the measurement of grip strength. The Grippit instrument is an electronic grip force measurement instrument. It measures the peak grip force and average grip force over 10 seconds. Maximum strength (N) and mean strength for 10 seconds (N) were measured and each hand was tested 3 times for both maximum strength and mean strength. The best of the 3 measurements was recorded and the average of the sum of the values for right and left hand is presented. The reliability of the test has been evaluated for healthy people, people with RA, and people with FMS; normative values for healthy women have been reported (26).

Joint mobility.

Joint mobility for the upper extremity was assessed functionally by an instrument measuring shoulder-arm movement impairment (27, 28), and assesses 5 common functional movements: hand raising, hand to opposite shoulder, hand to neck, hand behind back, and hand to seat. The test is designed with a score range from 1 to 6 for all movements. The scale steps refer to the ability to reach anatomic reference points. Thus the total score ranges from 5 to 30 for each shoulder, the higher the score the better the ability. The instrument was constructed for individuals with RA and the reliability and validity have been reported satisfactory for this group (27). The instrument has also shown sensitivity to change after physical therapy in patients with a shoulder fracture (29). The test includes pain assessment during motion by the Borg Category Ratio scale (CR-10 scale) (22), ranging from 0 to 10, where 0 equals “no pain” and 10 equals “extremely strong pain.” Because 5 functional movements were assessed, the total pain score for each shoulder ranges from 0 to 50, the higher score representing more pain. The CR-10 scale has revealed high correlation with the visual analog scale (VAS) in pain assessment, and the test-retest reliability has been shown to be high (22). Results are presented as the median of the sum of the values for right and left shoulder. Joint mobility for the lower extremity was evaluated using the Signals of Functional Impairment (SOFI) instrument (9). The assessment consists of 7 items for hand and upper limb function and 4 for lower limb function; it can be administered separately or as a total index. In this study, only the lower limb score was registered. The 4 items for the lower limb are ability to place heel above opposite knee when sitting on a chair, knee extension when lying supine, standing with 1 foot on a board that is balanced over a cylinder and tip the board so that the heel side touches the floor, and standing tip-toes without shoes on the floor. The scoring is on an ordinal scale with 3 alternatives for each item (0–2) based on the ability to perform the test items. The maximal total score for lower limb function is 16. A higher score indicates greater functional impairment. The instrument was originally constructed for patients with early RA and has shown to be reliable, valid, and sensitive to change for that group (9).

Pain intensity.

Pain intensity in the musculoskeletal system was measured with a 100-mm VAS where 0 was defined as “no pain at all” and 100 as “worst possible pain” (30).

Fatigue.

Fatigue was assessed with a modified Swedish version of the Chalder Fatigue Scale (CFS), which is a questionnaire measuring physical fatigue and mental fatigue. The original version (31) consists of 14 items (8 items for physical symptoms and 6 items for mental symptoms) with 4 response alternatives. It was constructed for use in both hospital and community populations and is reliable and valid (31). In the modified Swedish version, every item has 5 response alternatives graded from 0 to 4, where 0 is “much better than usual,” 2 is “as usual,” and 4 is “much worse than usual;” the total scale range is 0–56. A pilot study (Strömbeck et al, unpublished observations) has proved moderate to good test-retest reliability for 13 of the 14 items of the Swedish version of the CFS (n = 23, kappa = 0.55–0.80).

Functional disability.

For the evaluation of functional disability, we used the Swedish version of the Stanford Health Assessment Questionnaire (HAQ), which is self administered and designed to measure functional disability in patients with RA (32). It has also been used for patients with other rheumatic conditions (11, 33). The HAQ consists of 20 items divided into 8 subscales, measuring the patient's ability to perform daily activities. Difficulty in performing activities is graded on a 4-level ordinal scale. The average of the highest score for each subscale creates a disability index ranging from 0 to 3, where a higher score indicates greater disability. The Swedish version of HAQ possesses reliability and validity for patients with RA (32).

Anxiety and depression.

The Hospital Anxiety and Depression Scale (HAD) has been constructed to assess anxiety and depression in patients with somatic diseases (34). It contains 14 items for self assessment on a 0–3 scale. Seven items are intended to measure anxiety and 7 depression, independent of each other; the whole scale range is 0–21 each for anxiety and depression. A score of 8–10 on each subscale represents possible psychiatric morbidity and a score of more than 10 represents clinical anxiety or depression (34). The HAD has been used for screening for psychiatric morbidity in several patient groups (35–37) and its Swedish version has recently been used for patients with primary SS (8).

Statistics.

The sample size required for the study was estimated, setting the α level at 0.05 and the power at 80%, expecting a difference in VO2max between cases and control subjects of 4.5 ml/kg/minute (based on the results of the pilot study). A minimum of 27 subjects in each group was found to be needed for the 2-tailed test. To further enlarge the power, additional subjects were included. The results are given as mean or median values with standard deviations, confidence intervals, or interquartile ranges (IQRs) within parentheses. The groups were compared with the paired t-test, the Wilcoxon signed rank sum test, and the chi-square test. Correlation analyses were performed according to Spearman. Multiple linear regression analysis was employed to evaluate the independent effects of aerobic capacity, anxiety, depression, age, pain, and functional disability on CFS. Model assumptions were checked by means of residual analysis.

Ethics.

The design of the study was approved by the medical ethics committee at Lund University (no LU 367-99)

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

No significant differences between the primary SS group and the reference group were seen for weight, height, education, marital status, and work status. Besides the current medication for the primary SS patients, there was no difference in medication habits between the groups. There was a significant difference in the experience of generalized musculoskeletal pain (P < 0.01) and hand arthralgia (P < 0.01), with more intense pain in the primary SS group. The control group was significantly more active (P = 0.048) with regard to the level of physical activities and included significantly more smokers (P = 0.023) (Table 1).

Aerobic capacity.

A significant difference in aerobic capacity was found with the lower capacity in the primary SS group (VO2max = 28.7 versus 32.4 ml/kg/min; P = 0.013) (Table 2). Immediately after the bicycle test, the primary SS patients rated significantly higher (P < 0.01) on the RPE scale than the control group (Table 3).

Table 2. Differences between the primary SS group and age-matched control group in variables describing physical capacity*
VariableSS group n = 51 MeanControl group n = 51 MeanDifference (95% CI)P
  • *

    SS = Sjögren's syndrome; 95% CI = 95% confidence interval. P values determined by paired t-test.

Aerobic capacity    
 VO2max, ml/kg/min, n = 4828.732.4−3.7 (−7, −0.8)0.013
Isokinetic strength, Nm, n = 50    
 Knee extension 60°/sec, average of right and left107112−5 (−13, 4)0.246
 Knee flexion 60°/sec, average of right and left5156−5 (−9, −2)0.049
Isokinetic endurance, J, n = 50    
 Knee extension 240°/sec, average of right and left1,2571,344−87 (−175, 1)0.053
 Knee flexion, 240°/sec, average of right and left620712−92 (−158, −25)0.008
Standing balance, sec, average of right and left2528−3 (−5, −1)0.006
Grip strength, N, n = 50, average of right and left hand214259−45 (−68, −21)0.000
Grip strength, mean for 10 sec, N, n = 50, average of right and left171212−41 (−64, −17)0.001
Table 3. Differences between the primary SS group and age-matched control group in variables describing mobility, pain, fatigue, disability, mental disorder, and rating of perceived exertion*
Variable (score range)SS group n = 51Control group n = 51P
MedianIQRMedianIQR
  • *

    SS = Sjögren's syndrome; IQR = interquartile range; SOFI = Signals of Functional Impairment; CFS = Chalder Fatigue Scale; HAQ = Health Assessment Questionnaire; HAD = Hospital Anxiety and Depression Scale; RPE = Rating of Perceived Exertion. P values determined by Wilcoxon's signed rank sum test.

Shoulder mobility (10–60)     
 Median for right and left side58(55–59)59(56–60)0.003
Shoulder pain (0–100)     
 Median for right and left side1(0–18)0(0–0)0.000
Mobility lower extremities     
 SOFI (0–16)0(0–0)0(0–0)0.959
Fatigue     
 CFS (0–56)37(32–42)28(28–32)0.000
Disability     
 HAQ (0–3)0.13(0.0–0.63)0.0(0.0–0.0)0.001
Anxiety     
 HAD (0–21)8(4–12)5(3–8)0.002
Depression     
 HAD (0–21)4(2–9)1(0–4)0.000
RPE (6–20), n = 4816(14–18)14(13–15)0.005

Isokinetic muscle strength and endurance.

There was no difference in isokinetic muscle strength of the knee extensors, measured as peak torque at 60°/second. The difference in the knee flexor strength was significant (P = 0.049). There was no difference in isokinetic endurance of the knee extensors. The knee flexor endurance was, however, significantly lower in the primary SS group (P < 0.01) (Table 2).

Standing balance.

The result of the standing balance test showed a significant difference, with the primary SS group showing the lower value (25 versus 28 seconds; P < 0.01) (Table 2).

Grip strength.

The maximum grip strength as well as the mean grip strength for 10 seconds (average of right and left hand) were significantly lower (P < 0.01 in both analyses) in the primary SS group than in the control group (Table 2).

Joint mobility.

The primary SS group had significantly decreased mobility in the shoulder (58 versus 59 scale points; P < 0.01), and experienced a significantly higher pain level during shoulder motion (P < 0.01), although the differences were small (Table 3). Significantly more subjects in the primary SS group (P < 0.01) experienced pain during motion. The pain during motion was also given a higher rating (P < 0.01) in those with pain in the primary SS group. The median value for the pain rating among those who experienced pain was 17 (IQR 9–24) in the primary SS group (n = 26) and 9 (IQR 5.5–13.5) in the control group (n = 9).

There was no difference in the mobility of the lower extremities according to the SOFI index (Table 3).

Fatigue.

A significant difference was seen in the experience of fatigue according to CFS (P < 0.01), the primary SS group having the higher level of fatigue (37 versus 28 points) (Table 3)

Functional disability.

A significant difference in functional disability as measured by HAQ was noted, indicating that the women with primary SS experienced a decreased functional ability compared with the control group (P < 0.01) (Table 3)

Anxiety and depression.

The primary SS group had significantly higher levels on the anxiety (P < 0.01) and depression (P < 0.01) scales (Table 3). Eight subjects (15%) had a score of more than 10 on the depression scale and 17 (33%) had a score of more than 10 on the anxiety scale in the primary SS group, representing clinical depression and anxiety (34). In the control group, none scored more than 10 on the depression scale and 2 (3%) subjects scored more than 10 on the anxiety scale.

Correlations.

A significant correlation (r = –0.33, P = 0.022) of aerobic capacity (VO2max) with fatigue as measured by CFS was found in the primary SS group. No correlations of aerobic capacity with functional disability or mental aspects were seen. Age and aerobic capacity correlated significantly (r = –0.56, P < 0.01). Besides aerobic capacity, CFS correlated significantly to anxiety (r = 0.45, P < 0.01), depression (r = 0.56, P < 0.01), age (r = 0.31, P < 0.01), pain (r = 0.52, P < 0.01), and functional disability (HAQ) (r = 0.61, P < 0.01). Stepwise linear regression analysis, including functional disability (HAQ), depression (HAD), anxiety (HAD), pain (VAS), and age as independent variables, showed that depression (HAD), disability (HAQ), and age were independently associated with fatigue and together explained 45% of the variance in experienced fatigue (CFS) (Table 4). Because age and aerobic capacity were highly correlated (see above), an alternative regression model including aerobic capacity instead of age was also evaluated. In this regression model, disability (HAQ), aerobic capacity, and depression (HAD) were independently associated with fatigue and explained 50% of the variance in fatigue (CFS) (Table 5). There was a significant correlation between HAQ and grip strength (r = 0.67, P < 0.01).

Table 4. Stepwise linear regression analysis predicting fatigue (Chalder Fatigue Scale, total score 0–56) from 5 potentially explanatory variables (anxiety, depression, disability, age, pain) in the SS group, n = 50; R2 = 45%*
Independent variable (units of measurement)BSE(B)95% CICumulative R2P
  • *

    SS = Sjögren's syndrome; SE = standard error; 95% CI = 95% confidence interval; HAD = Hospital Anxiety and Depression Scale; HAQ = Health Assessment Questionnaire.

  • Estimate of regression coefficient (which reflects the change in the Chalder Fatigue Scale total score when the value of the variable under consideration increases by 1 unit). Excluded variables: anxiety, pain.

Depression, HAD (units, 0–21)0.540.22(0.10, 0.97)31.10.016
Disability, HAQ (units, 0–3)6.142.42(1.28, 11.0)40.20.014
Age (years)0.140.07(0.05, 0.27)45.20.043
Table 5. Stepwise linear regression analysis predicting fatigue (Chalder Fatigue Scale, total score 0–56) from 5 potentially explanatory variables (anxiety, depression, disability, aerobic capacity, pain) in the SS group, n = 47; R2 = 50%*
Independent variables (units of measurement)BSE(B)95% CICumulative R2P
  • *

    SS = Sjögren's syndrome; SE = standard error; 95% CI = 95% confidence interval; HAD = Hospital Anxiety and Depression Scale; HAQ = Health Assessment Questionnaire.

  • Estimate of regression coefficient (which reflects the change in the Chalder Fatigue Scale total score when the value of the variable under consideration increases by 1 unit). Excluded variables: anxiety, pain.

Disability, HAQ (units, 0–3)8.52.75(3.0, 14.1)38.30.003
Aerobic capacity VO2max (ml/kg/min)−0.280.12(−0.51, −0.04)43.90.022
Depression, HAD (units, 0–21)0.500.22(0.06, 0.95)49.90.026

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

This descriptive study presents information on physical capacity in women with primary SS based on clinical examinations and questionnaires. The results revealed small to moderate, significant reductions in aerobic capacity, joint mobility in the upper extremities, muscle function, and standing balance in women with primary SS compared with an age- and sex-matched control group from the general population.

The primary SS patients included in the present study fulfilled the EC criteria (5) for the diagnosis and had anti-SSA/SSB antibodies and/or autoimmune sialadenitis. At the time of investigation, they represented all available women at our clinic with autoimmune abnormality and fulfilling the eligibility criteria for this study. This reduces the selection bias as far as possible. A further strength is the representativness of our strict age- and sex-matched control group in relation to the general population. This is supported by the fact that weight and height are in concordance with the values for women aged 45–49 years previously tested for physical capacity in a study including 733 Swedish women (38).

Aerobic capacity was calculated by Åstrand's method (19), which is based on submaximal aerobic work. Submaximal tests are often used to predict maximal oxygen uptake when a maximal test is not possible or appropriate. The level of oxygen uptake was 11% less in the women with primary SS compared with the control group. According to the results of a Swedish investigation of aerobic capacity of 640 Swedish women from the general population (38), this decrease in aerobic capacity in the women with primary SS corresponds to an age difference of 10 years, i.e., from 40–45 years and 50–55 years, in Swedish women from the general population. The values of oxygen uptake reported for the women with primary SS of this study are higher than the values reported for 67 patients (24 men and 43 women) with RA of low to moderate disease activity and a mean (range) age of 53 (23–65) years (10), and 31 female patients with SLE without active disease in major organs with a median (range) age of 42 (25–51) years (13). In addition to having a reduced oxygen uptake, the women with primary SS in our study also experienced having to make a greater effort than the control group when performing the bicycle test, according to the RPE scale. Assuming that selection bias does not invalidate comparison between these studies, our data suggests that the patients with SS had an aerobic capacity that is intermediate to that in healthy people and patients with RA or SLE.

Both groups showed good shoulder arm mobility, close to normal values. However, there was a small (1 scale point) but significant difference between the groups. A decrease of 1 scale point means a small difference in mobility. However, the primary SS group more frequently experienced shoulder pain and rated the pain as more severe during the test, which might limit function when performing repetitive tasks.

The women with primary SS had a significantly lower strength and endurance of the knee flexors than the control subjects. A possible explanation of this could be the higher level of physical activity reported by the women in the control group, who to a greater extent participated in such activities as aerobics, bicycle exercise, and jogging, which ought to improve muscular strength and endurance in the lower limbs. Another explanation could be the lower level of aerobic capacity in the primary SS group because muscular endurance is dependent on oxygen uptake (39), which is also supported in our study, as there was a correlation between muscular endurance and aerobic capacity (data not shown). Maximal grip strength and mean strength for 10 seconds were also decreased in the primary SS group. Compared with the control group, both the peak and mean strength were reduced by approximately 20%. The values for the control subjects were similar to those published as normal values for women aged 40–49 (26). The hand arthralgia reported by the primary SS women might be one explanation for the reduced grip strength in this group. The decrease in standing balance for the primary SS compared with the control subjects was 11%. The mean value of the control group corresponded to the mean value of 153 male and female volunteers described in a study by Bohannon et al (25).

The women with primary SS were found to experience a slight reduction in physical ability as compared with the women in the control group. The median HAQ score was 0.13, which indicates a mild degree of limitation. As many as 45% had no problem in performing any of the activities included in the HAQ. One reason for the disability experienced could be the hand arthralgia and the reduced grip strength, because 5 of the 8 items of HAQ emphasize hand function and grip strength, and the HAQ score correlated (r = 0.68, P < 0.01). The median HAQ score (0.13) of the women with primary SS in our study is lower than that in SLE according to a study by Hochberg and Sutton (11). They reported a median HAQ score of 0.45 for 106 outpatients with SLE and a mean age of 41 years. Our values suggest that the disability in primary SS is intermediate between healthy controls and SLE patients.

The levels of anxiety and depression recorded for the primary SS patients in this study correspond to those of a recent Swedish study concerning anxiety and depression in primary SS (8). This study, by Valtýsdóttir et al, demonstrated significantly higher values for anxiety and depression in 67 primary SS patients (mean age 58, range 28–85 years) compared with a healthy control group (63 controls; mean age 57, range 54–60 years) as well as to a group of 38 RA patients (mean age 60, range 54–60 years).

Fatigue in primary SS is a symptom frequently reported (4, 6, 7) and the difference in fatigue between the groups of our study was expected and in accordance with results recently obtained by Barendregt et al (40). In our study, functional disability, depression, age, and aerobic capacity were possible explanations of experienced fatigue as measured by a modified Swedish version of CFS. A targeted program for physical activity, including aerobic training, would perhaps reduce fatigue. Such an effect is indicated for SLE patients in studies by Robb-Nicholson et al (41) and Daltroy et al (42), who reported that exercise resulted in an improved aerobic capacity and decreased fatigue. Disturbed sleeping habits in primary SS (43) was not evaluated in the present study.

Confounders, such as smoking and medication, could possibly influence our results. There was, however, no significant difference demonstrated between the primary SS group and the control group with respect to medication. On the other hand, there were significantly more smokers in the control group. In spite of this, the control group showed a higher oxygen uptake.

The women with primary SS participating in this study showed an impaired aerobic capacity, muscle strength and endurance in the flexors of the knee, standing balance, and joint mobility of the upper extremity compared with an age- and sex-matched reference group. There was a correlation between aerobic capacity and experienced fatigue. Whether or not a training program including exercises for flexibility, muscle strength, standing balance, and aerobic exercises would improve physical capacity and reduce fatigue remains to be investigated.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES
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